From Wikipedia:
The 8-track tape (formally Stereo 8; commonly known as the eight-track cartridge, eight-track tape, or simply eight-track) is a magnetic tape sound-recording technology that was popular in the United States[1] from the mid-1960s to the late 1970s, when the Compact Cassette format took over.[2][3] The format is regarded as an obsolete technology, and was relatively unknown outside the United States, the United Kingdom, Canada, New Zealand, Australia, and Japan.[2][3][4]
Stereo 8 was created in 1964 by a consortium led by Bill Lear of Lear Jet Corporation, along with Ampex, Ford Motor Company, General Motors, Motorola, and RCA Victor Records (RCA). It was a further development of the similar Stereo-Pak four-track cartridge introduced by Earl “Madman” Muntz, which was adapted by Muntz from the Fidelipac cartridge developed by George Eash. A later quadraphonic version of the format was announced by RCA in April 1970 and first known as Quad-8, then later changed to just Q8.
8 Track Tapes Blog 